Disk drives comprise a disk and a head connected to a distal end of an actuator arm which is rotated about a pivot by a voice coil motor (VCM) to position the head radially over the disk. The disk typically comprises a number of concentric data tracks each partitioned into a number of data sectors. Access operations are performed by seeking the head to a target data track, and performing a write/read operation on the data sectors within the data track. The disk typically comprises embedded servo sectors having position information recorded therein, such as coarse position information (e.g., a track address) and fine position information (e.g., servo bursts). A servo controller processes the servo sectors to position the head over the target data track.
Each data sector is typically assigned a physical block address (PBA) which is accessed indirectly through a logical block address (LBA) to facilitate mapping out defective data sectors. A PBA associated with defective data sectors may simply remain unmapped if found during manufacturing, or if a data sector becomes defective while in-the-field (grown defect), the LBA may be remapped to the PBA of a spare data sector (and the data relocated to the spare data sector). The process of initially mapping the LBAs to PBAs and mapping out defective PBAs is referred to as “formatting” the disk.
Scanning for defective sectors during manufacturing of the disk drive typically involves writing a special test pattern to each data sector (e.g., a 2T pattern) and reading the test pattern to identify defects. For example, a drop in the amplitude of the read signal may indicate a defect, or a defect filter matched to a defect signature may indicate a defect, or a number of bit errors exceeding a threshold may indicate a defect, etc. Defects may also be detected while the disk drive is deployed in-the-field, for example, if a data sector becomes unrecoverable using a sector level error correction code (ECC) due to a gown defect.